1. Field of the Invention
The present invention relates to a liquid crystal display having a back light unit capable of preventing luminescent line generated at the perimeter edge in the display area of a liquid crystal display and preventing slippage of sheets such as diffusion sheets by fastening firmly the sheets to a resin frame.
2. Description of the Related Art
FIG. 5 is an exploded perspective view showing a structure of a back light unit used as back light for a conventional liquid crystal display. FIG. 6 is a perspective view showing the back light unit after assembled. FIG. 7 is a cross-sectional view taken along the line Cxe2x80x94C in FIG. 6. FIG. 8 is a cross-sectional view taken along the line Dxe2x80x94D in FIG. 6. In those drawings, numeral 1 is a light guide plate that is a thin plate in shape and made of acrylic resin or the like, provided at the lower part of a liquid crystal display device (not shown). Numeral 2 is a diffusion sheet that diffuses rays of light from a light source evenly in a direction of the display side, provided along the upper surface of the light guide plate 1. The diffusion sheet 2 has a black-frame print portion 2a in the perimeter edge thereof. Numeral 3 is sheets provided between the diffusion sheet 2 and the light guide plate land comprised of, for example, a plurality of lens sheets, or a plurality of lens sheets and a plural of diffusion sheets. Numeral 4 is a reflecting sheet provided along the lower surface of the light guide plate 1. Numeral 5 is a lamp unit that is a light source, provided closely adjacent to at least one side surface of the light guide plate. Numeral 6 is a resin frame made of polycarbonate or the like for accommodating the light guide plate 1, the diffusing sheet 2, the sheets 3, the reflecting sheet 4 and so on. The lamp unit 5 is, as shown in FIG. 8, constructed to protect a cold cathode lamp 8 by surrounding or enclosing it with a lamp reflector 9 and a lamp cover 10. In addition, numeral 7 is a double-faced tape to fasten firmly the reverse side of the black-frame print portion 2a in the diffusion sheet 2 and the resin frame 6 together so that the diffusion sheet 2 and the sheets 3 may not slip.
In the conventional back light unit, the diffusion sheet 2 has a black-frame printed in its perimeter edge, and the double-face tape for preventing slippage of the diffusion sheet 2 and the sheets 3 is provided in the reverse side of the black-frame print portion 2a in the diffusion sheet 2. In some cases, the double-faced tape is provided on the longer side or on the shorter side of the resin frame 6 depending upon the use. All these are to prevent unevenness in luminance (hereinafter referred to as luminescent line), a phenomenon of rapidly intensified luminance arising at the perimeter edge of the diffusion sheet 2 that is a light emitting plane, that is, at the perimeter edge of the display area in a liquid crystal display device.
In the conventional liquid crystal display of above construction, the printing of a black-frame in the diffusion sheet 2 is used as the preventive measure against luminescent lines and taping of the double-faced tape 7 against slippage of the diffusion sheet 2 and sheets 3. In the diffusion sheet 2, however, an asperity work for forming roughness is applied onto its surface to diffuse rays of light, and therefore it is difficult to print the black-frame thereon when configuration of surface treatment or materials of the diffusion sheet 2 are not suited for printing. As a result, a problem exists in that adhesion of black-frame printing ink or paint to the diffusion sheet 2 is so insufficient that exfoliation of the print paint may take place, which affects negatively the performance of the liquid crystal display.
Further, with a recent increasing trend toward a larger effective display screen and a smaller frame around the screen, it has become more difficult to secure a sufficient space for the double-faced tape in the reverse side of the black-frame print portion 2a in the diffusion sheet 2.
Furthermore, in the manufacturing process of the conventional liquid crystal display, a problem exists in that the process is complicated and costly because the steps of printing the black-frames on the diffusion sheet 2 and taping the double-faced tape 7 are essentially required.
The present invention was made to solve the above-discussed problems and has an object of providing a liquid crystal display capable of preventing luminescent lines generated at the perimeter edge of the display area in the liquid crystal display device, capable of preventing slippage of the diffusion sheet and other sheets, and capable of being manufactured at a lower cost.
A liquid crystal display according to the invention comprises: a light guide plate that is a thin plate in shape and provided at a lower part of a liquid crystal display device; a light source provided closely adjacent to at least one side surface of the light guide plate; sheets including a plurality of diffusion sheets and lens sheets and provided along the upper surface of the light guide plate; a resin frame for accommodating the light guide plate and the sheets; and a lightproof tape taped on the perimeter edge of the top sheet of the sheets and on the upper side of the resin frame to fasten firmly the sheets and the resin frame together.
It is preferable that the diffusion sheet is provided on the top of the sheets.
It is preferable that the lightproof tape prevents luminescent lines generated at the perimeter edge of the display area of the liquid crystal display and, at the same time, prevents slippage of the sheets.
It is preferable that the lightproof tape is mainly made of polyester.
As described above, in the invention, by taping a lightproof tape on the perimeter edge of the top sheet of the sheets and on the upper side of a resin frame, it becomes possible to fasten firmly the sheets and the resin frame together and to prevent slippage of the sheets. At the same time, it also becomes possible to prevent luminescent lines generated at the perimeter edge of the display area in the liquid crystal display device. Furthermore, the method according to the present invention can omit two conventional steps of printing the black-frame and taping the double-faced tape, replacing these two steps with only one step of taping the lightproof tape, and consequently achieves a lower production cost as a result of a simplified manufacturing process.
Other objects, features and advantages of the invention will become more apparent in the course of the following description in connection with the accompanying drawings.